1. Field of the Invention
The embodiments of the invention generally relate to complementary metal oxide semiconductor (CMOS) devices, and, more particularly, to a field effect transistor (FET) used in a CMOS device.
2. Description of the Related Art
In FET devices, hole mobility is augmented when the channel is under compression in a direction parallel to the current. Electron mobility is augmented when the channel is under tension in a direction parallel to the current. Thus, there is the complication of the need to supply oppositely stressed materials for pFETs and nFETs if the switching speed is to be optimal for both simultaneously. Conventional CMOS devices typically involve either favorably straining only pFETs or nFETs while relieving the strain on the opposite type, or be depositing separate straining films for each type of FET, which is generally costly and complicated to fabricate. Therefore, there remains a need for a novel CMOS device that has oppositely stressed materials for pFETs and nFETs.